My boyfriend is always changing behaviour what to do?

My boyfriend and I have been together for four months. When we see eachother he always acts interested in me but after that in the last period he stopped texting me and is avoidant. I asked him many times is there any problem and he always says that he just doesn't have that much time and there isn't any problem with us. He hasn't texted me now for like 5 days and when I text he just gives me short answers. We didn't had any bad conflicts since our relationship started and he does this to me. After spending time together he acts like he doesn't care. What should I do? How to act?
My boyfriend is always changing behaviour what to do?
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